I am in the process of fine tuning my 04779 Holley, which is a 750 Double Pump variety. It came with #70 jets in the front and 80's in the back. The plugs were white white. I jumped to 74's in the front as a start. now #3 plug looks a tad rich, but others still look rather white. I am using the T/A Intake. Anyone stagger jetted before? I am thinking that I may be better off with different jets side to side and would love some tips before I tear it apart again! Thanks!
Plug Color sbbuick, I remember some years back CarCraft did a spray bomb rebuild on a Buick455 and the #3 plug was looking a little on the rich side while the other plugs looked "normal". I think it's probably OK because mine seem to do the same thing. The#1 and #7 plugs look to be burning a little leaner than the #3 and #5 plugs.I've tried leaning it out a little but still get the same results. Maybe this is something that is just inherant with the Buick engines(V8's)Don't know about the V6's . Maybe Dave at TA or Jim at Tri-Shield performance can shed some light on? o No:
Thanks, Jeff! That is helpful. I do know that dual plane intakes are more prone to lean / rich cylinder balance issues. It looks as if we are having the same issue. #1 is white and #3 is almost too rich. I am going to take a look at a pic of the T/A intake on their web site just to get an idea if the 1 and 7 cyls are on the opposite plane as the 3 and 5. I believe that they are, so I may try jetting up a number or two on that side. If inherent to any specific engines, I believe we'd have to include any V8's with dual plane intakes, which run on the same firing order as ours. I'll let you know what I find - especially after doing the actual jetting.
Thanks sbbuick I would really appreciate that!Keep us posted. I'm wondering if that's what Poston was talking about with the way their manifold is designed?So that it isolates certain cylinders?o No:
I think we're screwed Well, I E Mailed TA but never heard back so I took matters into my own hands! As we know, there is a "high" side plenum and a "Low" side on the TA 350" dual plane intake. Low side is drivers side and high is pass side. The Low drivers side feeds cyls 1,4,6 and 7. High side feeds cyls 2,3,5 and 8. These are my observations from last night. On my car, the really rich plugs are cyls 2,3 and 4 so we already have cyls from BOTH sides of the carb. The lean cyls are 1,6 and 8. #5 looked nearly perfect and #7 was only slightly rich (acceptable). In both cases, stagger jetting won't help because lean and rich cyls are found on both sides or halves of the intake plenum. I thought that maybe it was more of a front to rear of the engine deal, BUT #8 shows lean and #7 directly across from it - is on the rich side! Maybe if my Holley had the 4 corner idle feature I'd be Slightly better off. But that's just idle. I am not sure if there is anything left to do. Opinions, anyone??
SBBUICK I don't know how different your carb is from my new Demon 750 but I have the TA 350 intake on my engine also. I just changed the plugs 2 days ago and I've only had the carb on the engine for 6 days now. My observation is that I'm running a bit rich on all 8 cyl. and there is almost no dif in coloring from one plug to the next. I attribute this evan mixture to two things. Four courner idle mixture screws and a 1" phenolic spacer. The idle mixture circuit on a Demon is used all through the fuel curve not just at idle. The spacer helps to atomize the fuel better which I think helps distribute a more evan mixture to all cylenders. At this point I'm not sure weather to change the jets again for a leaner mixture or to change the pwr. valve. I need to get the vacume gauge inside the car to determine if I need a different pwr. valve before I go and mess with the jets again. One question I have is how did you get a 5 speed trany in your Custom and what problems did you encounter making the change. You can e-mail me with the answers to these questions if you don't want to post here. jasonbible@yahoo.com
Hey Jason, I wonder what jet numbers you have in that Demon. I went from stock jetting #70's in front and 80's in the back - to #74's in the front, back is unchanged. With the 70's the engine was lean all over. Now it's just certain cyls. I had a 1" spacer, but the Air Cleaner just slightly rubbed the underside of the hood, so I milled it down to 3/4". I also "ported" the spacer to take the shape of the intake. I mean, our intakes are more shaped like for a Q Jet. I left the top (carb side) of the spacer square but opened up the bottom so that the transition was much smoother. Knowing a little about airflow, I firmly believe that this "spacer mod" has Helped with mixture distribution, not hurt it. I don't think that your power valves are to blame. If the primary valve is opening too early, you'll foul the plugs after extended idle. Your cam would have to be quite huge (or something else would have to be terribly wrong) to give you such poor vacuum. If you know what jets and power valves you have, then yes, look at the vacuum gauge and see what's going on. In regards to the stick stuff: The 5 speed was the same length as the TH 350 I removed. I used GTO pedals and Chevelle linkage. Go with a new, steel flywheel. Stock ones are not safe, hard to find and are usually worn. Bellhousing is same BOP so that shouldn't be too hard to locate. The conversion isn't really all that tough, but LOOK AT THE ENGINE BLOCK for the threaded hole for the z bar. I had a '68 block that had it, but later engines may not. My Dad and I had to grind that part of the block flat, and then drill and tap the hole. Not very fun, and it's a damn good thing that I had the old '68 block to use as a reference. The holes are in the frame for the bracket for the Z bar on the other side. Also, when you take off the steering column plate from the fire wall, you can clearly see where the hole for the clutch rod needs to be cut. Use a metal hole saw. Let me know if you have any other questions. It's cool having a stick Skylark! Good Luck with it!
SBBuick The jetting in my demon is 73 in the primaries and 81 in the secondaries. The plugs I put in the other day are already starting to take on color which tells me it's still to rich. I'm going to change the jets again and see what that does. Demon always recomends keeping a 8 step variance between the primary and secondary jets. I'll let you know how things change as I make adjustments. By the way what is your name?
It's Andy. After reading about Demons' recommendation, I may jump back down to 72's primary. I don't like having such rich plugs even though some are still a little lean. We may be jumping the gun a little, though. I am sure that it's pretty darn cold in Utah right now. Should we be calibrating our carbs during the coldest month of the year? Lastly, what exhaust do you have? The more free flowing the exh, the leaner an engine tends to run. I have Hooker headers and the 2.5" mandrel bent system with very free flowing mufflers and H pipe. The car is kind of loud.
Andy It's not to cold here in Utah this year. It's currently about 54 deg. here. Now normally tuning in the winter is not the best way to do things as you will have to re-jet again this spring or summer. Demon recomends changing jets when ever you have a 1200 ft. change in altitude or 30 deg. in temp. Hummidity also plays a role in there. Since Utah can have a 20 to 30 deg. change in temp every day it doesn't make sense to change jets all the time. I think that I'm still to rich evan though it's cold to warm right now. When It gets hot I'm going to need to jet down again. That is if I'm remembering corectly which way to jet for hotter temps. Any ways It's at least a couple of months more of weather like this or colder so I don't want to wast a lot of gas by running too fat of a jet. I think that it's worth changing them now. To answer your other question I'm running stock ex. manifolds and a custom 2 1/2 in. duel exhaust with a H pipe cross over and Spin Tech mufflers. They breath very well and every one tells me they love the sound of my car. I can't complain.:grin: Also I just thought to ask does your engine idle above 1000 RPM or below?
I have my car set to idle at 600 RPM warm. It will idle lower, but this is a good setting to keep it running especially before the engine is completely warmed up. Today, I started it up and it actually idled at 500 RPM cold, after the choke had prematurely opened fully. This is with ALL heat blocked from the exhaust crossover in the heads. I love hot spark ignitions! Also - I think that cold weather tends to call for slightly richer jetting than warmer weather, if you forget about tendencies to knock and ping.
